Tires for each specific type of vehicle must have a normal internal pressure corresponding to that specific type of vehicle. In the event the internal pressure of a tire (that is, the tire pressure) is too low, it would have adverse influences on the safety in driving. In addition, due to the rotation of tire at high speed and the degraded air tightness of the tire valve, air inside the tire tends to leak gradually after the tire has been used over a long time, which results in insufficient tire pressure and thus adversely affects the safety in driving. Therefore, different types of tire pressure indicating devices have been developed to indicate tire pressure and warn the user when an insufficient tire pressure takes place.
Taiwanese New Utility Model Patent Publication. No. 186905 discloses a tire pressure warning device including a housing having a pressure-bearing membrane mounted therein; a push rod located above the pressure-bearing membrane; a compression spring providing the push rod with a restoring force; and a warning means. The warning means includes a first switch, which is a normally closed switch located above the push rod; a second switch, which is a normally open switch located above and electrically connected to the first switch; an emitter located between the push rod and the second switch and electrically connected to the first and the second switches; and a receiver provided at a location in sight of a driver. The internal pressure of a tire being detected actuates either the first or the second switch of the tire pressure warning device, making the emitter to emit a signal to the receiver and the tire pressure being displayed on the receiver.
Taiwanese New Utility Model Patent Publication No. 529559 discloses a membrane-type tire pressure gauge including a housing, a flexible membrane located in a receiving chamber of the housing, a push rod associated with the flexible membrane to move along with the flexible membrane, an inner sleeve also located in the receiving chamber of the housing, and a spring. The membrane-type tire pressure gauge is fixedly mounted to a tire valve to indicate the internal pressure of the tire.
Taiwanese New Utility Model Patent Publication No. 574977 discloses a tire pressure warning device including a connecting body having a cap screwed thereto. The connecting body is integrally molded and includes a connecting seat made of an electrically conductive material and a sleeve seat made of an electrically non-conductive material. The cap is screwed to the sleeve seat. The connecting body and the cap together define between them an inner space, in which emitting means and power supply means are provided. A conducting element, a pressure switch having a first contact and a second contact formed from a movable seat controlled by a membrane, an adjusting element, an elastic element located between the adjusting element and the movable seat, a first circuit connecting the first contact to the emitting means, and a second circuit connecting the second contact to the emitting means are provided between the emitting means and the power supply means. The connecting seat includes a connecting head separated by a separator with operating holes, and a conductor portion integrally formed on the connecting head. The sleeve seat includes a curtain portion enclosing an outer periphery of the connecting head when the sleeve seat is molded, and a seat body enclosing the conductor portion. The seat body is internally provided at one side opposite to the conductor portion with a fine adjustment space and a sliding space. The seat body is provided, at the fine adjustment space, with internal threads for an adjusting element to screw thereto, and that the seat body is provided, at the sliding space, with a round inner wall surface for the movable seat to slide upward and downward therein. The movable seat slides upward or downward depending on the pressure of the tire, so as to touch with or separate from the connecting seat and thereby electrically connects or disconnects a conducting circuit of the tire pressure warning device to achieve the warning function when an insufficient tire pressure takes place.
All the above-mentioned and other prior patents in connection with tire pressure measuring devices or tire pressure warning devices include an elastic element (spring) as the element to resist the internal pressure of the tire. That is, the elasticity of the elastic element is used to determine the pressure setting for measuring the tire pressure. Therefore, once an elastic element with a specific elasticity is selected for use, the pressure setting for measuring the tire pressure is determined. Since the pressure setting for measuring tire pressure determined in the above manner could not be arbitrarily adjusted once it is determined, the above-mentioned and other conventional tire pressure warning devices with such fixed pressure setting could be used with only one type of vehicle for which the tire pressure warning devices are particularly designed. For other types of vehicles or tires that require different pressure settings, users must expend more money to purchase additional tire pressure warning devices with corresponding pressure settings therefor.
The inventor therefore endeavors to develop a tire pressure warning device with adjustable pressure setting to overcome the drawbacks existed in conventional tire pressure warning devices.